In some vehicles, vacuum is used to operate or assist in the operation of various devices. For example, vacuum may be used to assist a driver applying vehicle brakes, to operate actuators for turbochargers, heating and ventilation systems, a drive line, and to purge fuel vapors, to name a few. If the vehicle does not produce sufficient vacuum naturally, such as from the intake manifold, then a separate vacuum source is required to operate such devices. An aspirator or an ejector can produce vacuum when supplied with manifold vacuum or boosted air from a turbo- or super-charger, respectively. The depth of vacuum produced will be a function of the motive pressure. An ejector, as used herein, is a converging, diverging nozzle assembly connected to a pressure source above atmospheric pressure. By passing pressurized air through the ejector, a low pressure region may be created within the ejector so that air can be drawn from a vacuum reservoir or may directly act on a device requiring vacuum, thereby reducing pressure within the vacuum reservoir or device requiring vacuum.
Typical ejectors cannot produce a suction pressure below atmospheric pressure when the motive pressure exceeds 192 kPa absolute and have no control over the motive flow rate. Boosted engines routinely have fluctuations in the boosted pressure, for example the flow coming from a compressor of a turbo- or super-charger. Thus, there is a need to improve the performance of an ejector on such a vehicle, in particular to regulate the flow of the boosted pressure for better control thereof, including providing a generally constant flow rate of boost pressure into the ejector and/or to provide greater depth of vacuum.